Forum Bugs - Cannot log in

Question

This forum is very difficult to use.
The following procedure has been exactly twice now:

I log in with email address and password.
I create a post (a question)
Someone answers my question
I call the page because I want to answer him and press Comment.
A dialog box tells me to log in.
I log in again and am successfully logged in.
I click on the Comment button again
Again a message appears that I should log in although I am already logged in!
After some tim i try again (with same username, password on same machine).
Log in success, but the system assigned me another username.
Therefore, I could no longer mark the answer as a solution.